Illustrative of variable displacement pumps are the gerotor type or vane type consisting of a controlled element and a control element which are eccentric to each other such as: U.S. Pat. Nos. 2,266,191 Granberg Dec. 16, 1941 (vane type) 2,649,739 Hufferd et al Aug. 25, 1953 (vane type) 2,678,607 Hufferd et al May 18, 1954 (vane type) 2,685,842 Hufferd Aug. 10, 1954 (vane type) 2,688,927 Nuebling Sept. 14, 1954 (gerotor) 3,026,810 Kubiak et al Mar. 27, 1962 (crescent or gerotor) 3,728,048 Ratliff Apr. 17, 1973 (vane type) 4,097,204 Palmer June 27, 1978 (crescent).
Characteristic of each of these variable delivery pumps whether vane operated or employing a gerotor with inner and outer gerotors, there is defined between the respective drive and driven elements controlled thereby an eccentric relationship which can in one manner or another be modified in some instances as to provide for the variable delivery of pressurized fluids from a pump. Generally speaking, it appears in each of these illustrations a means may be employed for regulating the eccentric position between the controlled and control elements which may be gears as in a gear pump or vanes in a vane type pump in order to preset the pump for a particular volume of delivery.